U.S. Pat. No. 4,997,706 describes the use of 1,1,1,2-tetrafluoroethane (R-134a) as a blowing agent which has a zero ozone depletion potential for closed cell rigid polyurethane foams in refrigeration applications where low thermal insulation K-factors are desirable. In other applications, however, where other foam properties such as buoyancy and dimensional stability are of paramount importance, a foam having good insulation properties may not satisfy these other requirements.
It would be desirable to manufacture a closed cell rigid polyurethane foam for use as a positive flotation device in watercraft. For this use, the foam must satisfy the U.S. Coast Guard requirements under 33 C.F.R. .sctn.183.114, which specifies that the flotation material must not lose more than five percent of its buoyant force as measured by ASTM D-2842 after being immersed for a specified amount of time in various media, such as gasoline vapor, gasoline, oil, and a five percent solution of trisodium phosphate in water. Under such rigorous conditions, the foam must be very dimensionally stable so as not to change its volume and must repel the media into which it is immersed to prevent picking up additional weight.